Slide-type electronic devices, such as mobile telephones, are known. Such electronic devices use flexible printed circuit boards (FPCs) to connect between the modules that move relative to each other during sliding. Typically, an FPC is designed as a flat cable with connectors at each end. When installed into the electronic device, the FPC forms a U-shape that allows it to follow the sliding motion by rolling along its longitudinal axis.
In systems where space is limited, the FPC is provided with wires on each side of the flexible substrate so as to reduce the width of the FPC.
Flexible printed circuit boards are known that use two parallel substrates between two connectors, wherein each of the substrates carries a layer of wires between the connectors. In such examples, the substrates are joined together at their two ends, near the connectors so as to provide a gap between the two substrates between the two ends of the FPC. Such an example may be known as an air gap FPC.
However, the use of air gaps in slide application devices can create some challenges to the dynamic performance. Due to the FPC manufacturing process, both conductor layers/substrates in the FPC are the same length. This means that when the FPC is folded in use, a “kink” (also known as “flex buckling”) can appear in the inner layer when the FPC is assembled in the electronic device. The kink can severely affect the dynamic durability of the flexible printed circuit board, and can also generate an unwanted clicking sound during movement of the slide.
A known way to resolve the “kink” problem is to create a permanent kink in a strategic position of the inner conductor layer using a pre-bend technique. This pre-bend/kink effectively shortens the inner radius layer to eliminate or reduce problems created by using an air gap flexible printed circuit board. However, the crimping process that is required to create the permanent kink can damage the flex, and special machinery may be required for semi-automatic pre-bend application to ensure the pre-bend is made in the same way every time.
A conventional two-layer build-up may not withstand the rolling motion often enough to be suitable for use in some devices, such as mobile telephones.
The listing or discussion of a prior-published document or any background in this specification should not necessarily be taken as an acknowledgement that the document or background is part of the state of the art or is common general knowledge. One or more aspects/embodiments of the present disclosure may or may not address one or more of the background issues.